Diesel heat pump

ABSTRACT

A diesel powered emergency electrical generator for providing a back-up power supply for critical building systems. The diesel engine is heated by a heat pump in series with a resistance heater. The heat pump is normally cycled on and off to maintain the desired engine temperature and the resistance heater is employed only when the heat pump is unable, for whatever reason, to maintain the desired engine temperature. The heat pump includes a refrigerant to coolant condenser and an air to refrigerant evaporator and includes a centrifugal pump which operates continuously to maintain a continuous circulation of coolant through the engine and through the heat pump.

This invention relates to means for providing heat to the coolantflowing through the jackets of an internal combustion engine and, moreparticularly, relates to a means for providing heat to the coolant ofthe diesel engine of a diesel powered emergency electrical generatorassembly.

Many commercial and industrial facilities have one or more dieselpowered emergency electrical generators to provide a back-up powersupply for critical systems in the building such as elevators, lightsand computer equipment.

A critical requirement of diesel engines for instantaneous starting andproper performance is to maintain the engine at a predeterminedtemperature. Typically, the recommended temperature is approximately100° F. The most common method of providing heat to maintain therequired engine temperature is with a resistance electrical heatingelement. The element is typically located somewhere within the liquidcooling system of the engine and heat is transferred by thermosiphonaction through the water jackets. A thermostat operates to shut off theresistance heating element when the engine temperature reaches apredetermined set point temperature. Whereas these electrical resistanceheaters are effective to maintain the required predetermined enginetemperature in most applications, they typically operate a very highpercentage of the total standby and operating time of the engine andhave proven to be rather energy inefficient.

SUMMARY OF THE INVENTION

This invention is directed to providing a more energy efficient systemfor maintaining an internal combustion engine at a predetermined setpoint temperature.

More particularly, this invention is directed to providing an improvedengine heater for the diesel engine of a diesel powered emergencyelectrical generator set.

Broadly considered, the invention provides an internal combustionassembly including a water cooled internal combustion engine havingcombustion chambers and internal coolant conduit means extendingtherethrough between a coolant inlet and a coolant outlet in heatexchange relation to the combustion chambers; external coolant conduitmeans extending outside of the engine between the coolant outlet and thecoolant inlet to form a closed coolant loop with the internal coolantconduit means; and heater means operative to pass a heated fluid in heatexchange relation to the external coolant conduit means to heat thecoolant flowing therethrough. This arrangement has proven to provide anextremely energy efficient manner for maintaining the internalcombustion engine at a predetermined set point temperature.

According to a further feature of the invention, the heater meanscomprises a heat pump including a condenser in which gaseous refrigerantis passed in heat exchange relation to the external coolant conduitmeans and an evaporator in which ambient air is passed in heat exchangerelation to the refrigerant.

According to a further feature of the invention, the assembly furtherincludes an electrical resistance heater in heat exchange relation tothe coolant flowing through the external coolant conduit means. Theresistance heater, which may comprise an existing resistance heaterpreviously installed on the engine, is arranged in series with the heatpump and is associated with a portion of the external conduit meansbetween the heat pump and the coolant inlet. This arrangement provides aredundant arrangement whereby either the heat pump or the resistanceheater may be utilized to maintain the engine at the predetermined setpoint temperature.

According to a further feature of the invention, the resistance heateris deenergized in normal usage and the work of heating the coolant andthereby the engine is done by the heat pump. In the disclosedembodiment, the resistance heater is controlled by a thermostat and isenergized only in the event that the coolant leaving the heat pump issensed to have a temperature below a desired temperature. With thisarrangement, the heat pump cycles on and off in response to sensedinternal engine temperature to normally maintain the desiredpredetermined internal engine temperature and the resistance heater isavailable as a back-up or stand-by in the event that the heat pump isunable to maintain the desired temperature.

According to a further feature of the invention, the cool air leavingthe evaporator is directed to the generator driven by the engine so asto cool the generator. This arrangement allows the ambient air to beutilized to both heat the internal combustion engine and cool thegenerator to further contribute to the overall energy efficiency of theinvention system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the invention internal combustionassembly; and

FIG. 2 is a schematic view of the invention internal combustionassembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention internal combustion assembly, broadly considered, includesan internal combustion engine 10; a generator 12; a heat pump 14; aresistance heater 16; external coolant conduit means 18; and internalcoolant conduit means 20.

Internal combustion engine 10 may take any known form but, in thecontemplated commercial embodiment, comprises a diesel engine of knownconstruction including cylinders 22 in which a suitable fuel/air mixtureis supplied in a known manner and in which the fuel/air mixture isignited in known manner to provide the power output for the engine.Interconnected cooling jackets 24 surround each cylinder in a knownmanner.

The generator 12 is of known form and is driven by a shaft 26 fromengine 10. Generator 12 may, for example, constitute the emergencyelectrical backup power supply for critical systems in a building suchas elevators, lights and computer equipment.

Heat pump 14 includes a housing 28; a water to refrigerant heatexchanger or condenser 30; an air to refrigerant heat exchanger orevaporator 32; an expansion valve 34; a compressor 36; and a centrifugalcirculating pump 38. A suitable refrigerant is circulated in seriesthrough heat pump 14 from expansion valve 34, through the coil 40 of theevaporator 32, through an accumulator 42, through a dryer 44, throughcompressor 36, through the coil 46 of condenser 30, and back toexpansion valve 34.

More specifically, the refrigerant, with its temperature raised bysensible energy and compression is pumped by compressor 36 in gaseousform into condenser 30. As the refrigerant passes through the condenserit changes phase to a liquid and gives up its phase change energy tocoolant flowing through the condenser. The liquid refrigerant leavingthe condensor 30 flows to expansion valve 34 and is converted to aliquid/gas mixture leaving valve 34. The liquid/gas mixture then entersevaporator 32 at well below ambient temperature, absorbs heat from theambient air and leaves the evaporator in totally gaseous phase,whereafter it enters compressor 36 to begin another cycle.

A blower 48 operates to suck air in through a filter 50 located in anair inlet 52 for passage over evaporator coil 40 and discharged throughan air outlet 54. A condensate pump 56 cooperates with a condensatedrain 58 to remove condensate from evaporator 32.

Resistance heater 16 is of known form and includes an electricalresistance heating element suitably positioned in heat exchange relationto coolant flowing therethrough so that when the resistance heater isenergized the coolant is heated by the resistance heater.

External coolant conduit means 18 includes a conduit 60, a conduit 62,and a conduit 64. Conduit 60 extends from a coolant outlet 66 in thelower portion of the block of engine 10 and through housing 28 of heatpump 14 for communication with the inlet of circulating pump 38. Conduit62 extends from the outlet of pump 38, passes through coil 46 ofcondenser 30, and then passes outwardly through housing 28 forcommunication with the lower end of resistance heater 16. Conduit 64extends from the upper or outlet end of resistance heater 16 to acoolant inlet 68 in the upper portion of the block of engine 10.Internal coolant means 20 includes suitable passage means 70 defined inthe engine block and providing fluid communication between coolant inlet68 and jackets 24, between the several jackets 24, and between thejackets 24 and coolant outlet 66 so as to define, in combination, acontinuous coolant passage extending from coolant inlet 68 to coolantoutlet 66.

The internal combustion assembly of the invention further includes acontrol means seen schematically at 72. Control means 72 includes anon/off switch 74; a thermostat assembly 76; and a further thermostatassembly 78. Thermostat assembly 76 includes a sensor element 76a incommunication with the coolant leaving the engine block at coolantoutlet 66. Thermostat assembly 78 includes a sensor element 78a forsensing the temperature of air entering the air inlet 52 of evaporatorheat exchanger 32.

The invention internal combustion assembly further includes athermostatic assembly 80 including a sensor element 80a for sensing thetemperature of the coolant entering resistance heater 16.

OPERATION

As indicated, the invention internal combustion assembly is intended toprovide an emergency electrical back-up power supply for criticalsystems in buildings such as elevators, lights and computer equipment.In a typical situation, the engine 10 is not operating but rather is ona stand-by basis. It is imperative however that the engine temperaturebe maintained at a certain optimal level to provide ready start-up andoptimal performance at such time as the internal combustion assembly iscalled upon to provide back-up power. Accordingly, pump 38 operatescontinuously to provide a continuous circulation of coolant throughexternal conduit means 18 and internal conduit means 20 which togetherprovide a closed coolant loop. Thermostat assembly 76 continuouslysenses the temperature of the coolant leaving engine 10 and switchesheat pump 14 on and off in response to the sensed coolant temperature.When the coolant leaving outlet 66 drops below a predetermined set pointtemperature corresponding to the desired temperature at the engineblock, thermostat 76 functions to close a circuit to the motors drivingcompressor 36 and blower 48 so that the heat pump becomes operative toextract heat from the air flowing through evaporator 32 and impart phasechange heat to the coolant flowing in conduit 62 through condensor 30.The heat pump continues to operate until thermostat 76 senses that thecoolant leaving coolant outlet 66 has achieved the set point temperaturewhereupon the thermostat functions to deenergize the heat pump.

Whereas the prior art resistance heater is typically operated close to100% of the time, the invention internal combustion assembly, in atypical installation, has been found to operate between 36% and 44% ofthe time under actual test conditions, and in comparisons with prior artresistance heaters, the invention internal combustion assembly has beenfound to provide at least a 50% reduction in energy consumption tomaintain a given engine block temperature.

The invention internal combustion assembly also provides, as aby-product, dry cool air and this dehumidified cool air can be directedby ducting to adjacent switch or gear rooms or, as shown by the ducting82, to the generator 12 being driven by engine 12. The invention systemthus functions to extract heat from the ambient air and impart it to thecoolant flowing through the engine to heat the coolant and furtherfunctions to direct the cooled air into heat exchange relation to thegenerator driven by the engine so as to cool the generator. Asindicated, the cooled dehumidified air may alternatively be directed toother equipment in the mechanical rooms associated with the engineassembly.

It will be seen that resistance heater 16 is in series with the heatpump 14 is is situated between the heat pump and the inlet 68 to theengine. Heater 16 is not utilized in the normal operation of theinvention system but rather provides a redundant or back-up source ofheat for the engine coolant. Specifically, thermostat 80 continuouslysenses the temperature of the coolant entering the resistance heater 16and, in response to a sensed coolant temperature that is 5° lower thanthe desired temperature of the coolant entering the heater 16, theresistance heater is energized to provide supplemental electricalresistance heat to the coolant.

Thermostat 78 functions to totally deenergize the heat pump in the eventthat the temperature of the air entering inlet 52 drops below apredetermined value. For example, thermostat 78 may be set to disablethe heat pump when the temperature of the air entering inlet 52 dropsbelow 48° F., which corresponds to the value at which it is no longerpractical to attempt to extract usable heat from the ambient air. Atsuch time as the heat pump is disabled by the thermostat 78, means (notshown) automatically function to energize resistance heater 16 so thatthe engine coolant is maintained at the desired temperature.

The invention will be seen to provide a extremely energy efficientsystem for maintaining an internal combustion engine at a predeterminedset point temperature. More particularly, the invention will be seen toprovide an improved engine heater for the diesel engine of a dieselpowered emergency electrical generator set. The improved engine heateroperates to maintain the diesel engine at a desired engine temperaturewith substantially less energy consumption than that required by artresistance heaters and, as an added benefits, cool dehumdified air whichmay be advantageously employed with respect to associated equipment.

I claim:
 1. .[.An.]. .Iadd.A liquid cooled .Iaddend.internal combustion.Iadd.engine .Iaddend.assembly comprising:A. a liquid cooled internalcombustion engine having combustion chambers and internal coolantconduit means extending therethrough between a coolant inlet and acoolant outlet in heat exchange relation to said combustion chambers; B.external coolant conduit means extending outside of said engine betweensaid coolant outlet and said coolant inlet and coacting with saidinternal coolant conduit means to form a closed coolant loop; and C..Iadd.means operable independently of said engine for maintaining acoolant circulating through said coolant conduit at above at least apredetermined minimum temperature means, including: .Iaddend.heatermeans operative to deliver a refrigerant in gaseous form to saidexternal coolant conduit means and condense the refrigerant as it flowsin heat exchange relation to said external conduit means to thereby giveup the phase change heat to the coolant flowing through the externalconduit means.
 2. The internal combustion assembly according to claim 1wherein:D. said heater means comprises a heat pump; E. said means fordelivering said refrigerant in gaseous form to said external coolantconduit means comprises the condenser of said heat pump; and F. saidheat pump further includes(1) an evaporator including means for passingsaid refrigerant in heat exchange relationship to ambient air, (2) acompressor for receiving said refrigerant as it leaves said evaporatorin gaseous form, and (3) an expansion valve for receiving saidrefrigerant in liquid form as it leaves said condenser.
 3. An internalcombustion assembly according to claim 1 wherein said assembly furtherincludes:D. an electrical resistance heater in heat exchange relation tothe coolant flowing through said external coolant conduit means.
 4. Aninternal combustion assembly according to claim 3 wherein:E. saidresistance heater is arranged in series with said heater means and isassociated with a portion of said external conduit means between saidheater means and said coolant inlet.
 5. An internal combustion assemblyaccording to claim 4 wherein said assembly further includes:F. controlmeans including means for sensing an internal temperature of said engineand operative to energize said heater means in response to a sensedtemperature below a predetermined set point temperature and deenergizesaid heater means in response to a sensed temperature above said setpoint temperature.
 6. An internal combustion assembly according to claim5 wherein:G. said control means further includes means for sensing thetemperature of said coolant as it arrives at said resistance heater andoperative to energize said resistance heater in response to a sensedtemperature below a predetermined set point temperature.
 7. A heater foruse with a stationary diesel engine to maintain the engine at apredetermined temperature, said heater comprising:A. a housing; B. aninlet for receiving coolant from said engine; C. an outlet fordischarging coolant for delivery to said engine; D. a conduit extendingwithin said housing between said inlet and said outlet; E. a condensercoil in heat exchange relation to said conduit; F. means for passingambient air through said housing; G. an evaporator coil in heat exchangerelation to said ambient air; and H. means for moving a phase changefluid serially and cyclically through said evaporator and condensercoils to heat the engine coolant flowing through said conduit.
 8. Theheater according to claim 7 wherein:I. said moving means includes anexpansion valve between the outlet of said condenser coil and the inletof said evaporator coil and a compressor between the outlet of saidevaporator coil and the inlet of said condenser coil.
 9. A heateraccording to claim 8 wherein:J. said heater further includes acirculating pump in said conduit for circulating engine coolant throughsaid heater from said inlet to said outlet.
 10. A heater according toclaim 9 wherein:K. said pump is disposed within said housing betweensaid inlet and said condenser coil.
 11. A heater according to claim 9wherein:K. said passing means includes:1. an air inlet in said housing,2. an air outlet in said housing,
 3. air conduit means extending betweensaid air inlet and said air outlet, and
 4. a blower positioned in saidair conduit means adjacent said air outlet; and I. said evaporator coilis positioned in said air conduit means between said air inlet and saidblower.
 12. An engine and generator assembly comprising:A. a liquidcooled internal combustion engine; B. a generator driven by said engine;C. means for extracting heat from the ambient air an imparting it to thecoolant flowing through said engine whereby to cool the ambient air andheat the coolant; and D. means for directing the cooled air into heatexchange relation to said generator to cool said generator.
 13. Anengine and generator assembly according to claim 12 wherein:E. saidmeans for extracting heat comprises a heat pump including a refrigerantto engine coolant condenser and an air to refrigerant evaporator; and F.the air leaving said evaporator is directed into heat exchange relationwith said generator.
 14. A heater for use with a stationary dieselengine to maintain the engine at a predetermined temperature, saidheater comprising:(A) a housing; (B) an inlet for receiving coolant fromsaid engine; (C) an outlet for discharging coolant for delivery to saidengine; (D) a conduit extending within said housing between said inletand said outlet; (E) a condenser coil in heat exchange relation to saidconduit; (F) means for passing a heat exchange fluid through saidhousing; (G) an evaporator coil in heat exchange relation to said heatexchange fluid; and (H) means for moving a phase change fluid seriallyand cyclically through said evaporator and condenser to heat the enginecoolant flowing through said conduit.